This invention relates to thermal and noise insulation of the axial end walls of heated or cooled temperature controlled cylinders, as for example the type of rotatable cylinders used in the paper manufacturing industry, wherein a web of paper material passes over the peripheral convex surface of a heated dryer cylinder and absorbs heat from the cylinder.
In the process of manufacturing paper products, wet paper is moved in a web across a plurality of heated cylinders, and the heated cylinders progressively dry the paper which eventually emerges as a dryer product. The dryer cylinders vary in length and in diameter, but a common range of lengths and diameters of dryer cylinders would be between 1 and 40 feet in length and between 1 and 30 feet in diameter. The normal rotational velocity of operating dryer cylinders is between 100 and 10,000 surface feet per minute, and a common temperature range for dryer cylinders would be between 100.degree. F. and 600.degree. F.
The dryer cylinders can be heated from various heat sources, with a common heat source being superheated steam at a temperature sufficient to heat the cylindrical convex surface of the dryer cylinder to the desired temperature. The steam is transmitted under pressure through the axles of the dryer cylinders to heat the inside of the dryer cylinders.
Since the web of paper makes continuing contact with the external convex surface of the dryer cylinder wall during the operation of the dryer cylinder, a major portion of the heat applied to the cylindrical wall of the dryer cylinder is absorbed by and taken away by the paper; however, the web of paper does not contact the axial end walls of the dryer cylinder, and the heat from inside the dryer cylinder that is transferred through the axial end walls is lost to the atmosphere.
Some attempts have been made to insulate the axial end walls of heated dryer cylinders. For example, U.S. Pat. No. 2,571,426 discloses the mounting of a heat insulating asbestos disc to the inner face of the axial end wall of a dryer cylinder, while U.S. Pat. No. 4,241,518 discloses clamping semi-circular panels to the connector bolts of the axial end walls of a dryer cylinder. While it appears that the attachment of insulation structures to the internal surfaces of the axial end walls of a dryer cylinder would function to retard the loss of heat from a dryer cylinder, it appears that such a structure would be difficult to install and would be hidden from inspection unless the manhole cover was removed from the dryer cylinder. While it appears that external heat shields could be applied to the external surfaces of an axial end wall of a rotatable dryer cylinder by attaching the heat shields to the bolts that attach the axial end wall to the cylindrical wall, it is undesirable to do so since the bolts must contain the axial end wall in position against the pressure of the high pressure superheated steam within the dryer cylinder and the loosening or otherwise adjusting of the bolts might result in a safety hazard due to the bolts parting from the dryer cylinder during rotation or due to steam leakage between the cylindrical wall and the axial end wall of the dryer cylinder. Additionally, many of the dryer cylinders which contain fluid under pressure are regulated by ASME pressure vessle codes which limit the use of the connector bolts for purposes other than connecting the end wall to the cylindrical wall of the assembly.
The use of nonflexible rigid insulator panels with the axial end walls of temperature controlled rotatable cylinders apparently requires the insulator panels to be constructed for a particular end wall shape so the nonflexible insulator panels in some instances would be usable for only one model dryer cylinder, and the rigid insulator panels apparently would require that the panels be formed in a multiple number of parts that would have to be assembled about the axle of the dryer cylinders when being applied to the axial end wall of the dryer cylinder in its plant operating configuration.
The usual construction of a heated dryer cylinder for use in a paper making process is to have the axial end wall formed in a precision fit with respect to the cylindrical wall of the dryer cylinder. The connector bolts can be tightened in a pattern to draw the axial end wall onto the cylindrical wall, and when the axial end wall is to be removed from the cylindrical wall, the connector bolts are loosened and threaded jack screw openings usually are present in the axial end wall so that externally threaded jack screws can be rotatably inserted into the jack screw openings to bear against the end of the cylindrical wall and progressively push the axial end wall off the cylindrical wall. When the axial end wall is properly mounted on the cylindrical wall and the dryer cylinder is ready for normal operation, the jack screws usually are removed from the jack screw openings of the axial end wall.